The present invention relates to a control device for a back-up memory set in a vehicle control computer which is used for fuel injection control, ignition control and other electronic controls of a vehicle engine.
It has been well known that vehicle engines can be electronically controlled depending on the running condition of the vehicles.
Such an electronic control unit for vehicle engines is composed of a computer which contains a back-up memory for temporarily storing various types of measuring data and processed data.
The vehicle control computer is set in operation when the ignition switch is turned on. Therefore, the data write control for the back-up memory is executed depending on whether the ignition switch is on or off. More specifically, when the ignition switch is turned on, an increase of power source voltage is sensed by the computer hardware and the computer enables the write operation or write enable state to the back-up memory when the power voltage increases above a specific or predetermined voltage.
When the ignition switch is turned off, the hardware senses a decrease in the power voltage and the computer inhibits or disables the write operation to the back-up memory when the power voltage decreases below the specific voltage.
With such an arrangement, when the power voltage drops below the specific voltage during the course of writing data into the back-up memory, the data writing operation into the back-up memory is inhibited. For this reason, there is a danger that the contents of the back-up memory may be destroyed. Thus, care needs to be taken to protect memory contents.